A Loyola study of high school students provides new evidence that a person’s circle of friends may influence his or her weight.
Students were more likely to gain weight if they had friends who were heavier than they were. Conversely, students were more likely to get trimmer — or gain weight at a slower pace — if their friends were leaner than they were.
Results of the study by David Shoham, PhD, and colleagues are published in the journal PLoS ONE. Shoham is an assistant professor in the Department of Preventive Medicine & Epidemiology of Loyola University Chicago Stritch School of Medicine.
A student’s social network also influences how active he or she is in sports. (By social networks, researchers mean face-to-face friends, not Facebook friends.)
“These results can help us develop better interventions to prevent obesity,” Shoham said. “We should not be treating adolescents in isolation.”
The study was designed to determine the reason why obesity and related behaviors cluster in social networks. Is it because friends influence one another’s behavior? (This explanation is called “social influence.”) Or is it simply because lean adolescents tend to have lean friends and heavier adolescents tend to have heavier friends? (This explanation is called “homophily, or more informally, “Birds of a feather flock together.”) Researchers used a sophisticated statistical technique to determine how much of the link between obesity and social networks is due to social influence and how much is due to homophily. This statistical technique is called “stochastic actor-based model,” or SABM.